An engine may be operated with a high concentration of exhaust gas recirculation (EGR) to reduce engine emissions and engine pumping losses. However, it may be more difficult to ignite highly diluted air-fuel mixtures. One way to increase the probability of igniting a dilute mixture is to increase an amount of energy delivered to a spark plug. The amount of energy supplied to a spark plug may be increased via increasing the inductance of a coil supplying energy to the spark plug. Nevertheless, it may still be difficult to ignite a diluted air-fuel mixture if the spark energy is delivered over a short time period. On the other hand, two ignition coils may be configured to supply spark energy to a spark plug, thereby increasing the energy delivered to the spark plug and spark duration so that the possibility of igniting a dilute air-fuel mixture may be increased. Although two ignition coils may increase the possibility of igniting the air-fuel mixture, cost of diagnosing degradation of two ignition coils via hardware signals and amplifiers may be prohibitive. Therefore, it may be desirable to provide a way of diagnosing two ignition coils that supply energy to a sole spark plug without having to significantly increase diagnostic hardware.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an ignition system, comprising: receiving engine data to a controller; judging a presence or absence of misfire in a cylinder during a cycle of the cylinder based on the engine data via the controller; and indicating ignition coil degradation and combusting air and fuel in the cylinder via the controller in response to absence of misfire in the engine cylinder during the cycle of the cylinder.
By realizing that a cylinder may combust air and fuel even when one of two ignition coils are degraded, it may be possible to diagnose ignition coil degradation without added sensors or hardware. For example, after a first indication of a misfire episode in a cylinder, ignition coil dwell may be increased to reduce a possibility of misfire in a cylinder if the cylinder's ignition coils are not degraded. Sufficient spark energy may be present in the cylinder to ignite an air-fuel mixture, even when high EGR levels are in the cylinder, when spark energy is increased via increasing dwell time of two ignition coils. In this way, increasing the dwell time of two ignition coils may provide insight as to whether or not ignition coils are degraded. If dwell time of the two ignition coils is increased and misfire is still present in the cylinder, EGR delivered to the cylinder may be decreased to ascertain if the cylinder will fire (e.g., combust air and fuel) with a lower EGR amount. If the cylinder fires, it indicates that one ignition coil is operable, but the second ignition coil is degraded. If the cylinder does not fire, it indicates that both ignition coils and/or their circuitry are degraded.
The present description may provide several advantages. For example, the approach provides for diagnosing operation of two ignition coils without additional hardware. Further, the approach does not require individually commanding ignition coils to determine if a single ignition coil is degraded. Additionally, it may be possible to diagnose a degraded ignition coil in a shorter amount of time and/or in a fewer actual total number of cylinder cycles.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.